Seal for electric devices



Aug. 14, 1928.

A. W. HULL SEAL FOR ELECTRIC DEVICES Filed Aug. 23, 1926 HI w YU O & YVIMW A .mhm w H A Patented Aug. 14, 1928.

UNITED STATES PATENT OFFICE.

ALBERT W. HULL, OF SCHENECTADY, NEW YORK, ASSIGNOB '10 GENERAL ELECTRIC COMPANY, A. CORPORATION 01 NEW YORK. V

SEAL FOR ELECTRIC DEVICES.

Application filed August 23, 1926. Serial No. 130,831.

My present invention relates to improvements in gas-tight seals of the type described in the patent to Mackay No. 1,456,110 granted May 22, 1923.

In the employment of seals for high power vacuum tubes, it is desirable that the amount of glass employed in connection with the seals should be as small as possible, consistent with obtaining the proper degree of insulation required, owing to the fact that tubes of this type are subjected'to widely varying temperatures and sometimes to mechanical shocks, both of which tend to destroy the insulating qualities of the seal and to permit the leakage of gas.

While a seal of the type described in the Mackay atent is adapted for use in power tubes, I ave found it desirable to provide a seal which is even more rugged than that described in the patent and which may more readily be built up to pro ide any degree of insulation desired and yet remain gas-tight 7 under all conditions of use. In carrying out my invention, I provide a seal having a conductive core surounded by a plurality of alternate, concentric layer of-thin glass and metal, which may be swaged or castto provide a gas-tight seal, each glass layer making a gas-ti ht joint with adjoinin metal surfaces an the glass layers of tlie seal being so thin and long that if chance cracks develop in the seal they do not run the entire length thereof.

In the accompanying drawing, Fig. 1

" shows a perspective view of an electric discharge device rovided with seals at its opposite ends, w ile Figs. 2 and 3 are cross sections, on an enlarged scale, of the seals employed at the opposite ends of the discharge device, the latter figure embodying the features of my invention.

Referrin to the drawing, I have illustrated in Fig. 1 a discharge device which, in the present instance, is a low pressure argon rectifier of the half wave t pe. The rectifier comprises a cylindrical errous metal container 1, a thoriated filament 2 and an anode 3. The ends of the container are closed by seals 4 and 5. Seal 4 is similar to that described in the Mackay patent and comprises a pair of conductive cores 6 and 7 threaded through glass cylinders or insulators 8 and 9. The insulators fit in a ferrous metal plug or-shell 10 which is bored to receive the insulators 8 and 9 and counter bored to provide an outwardly extending flange 11. The metal plug or shell 10 and the surface of the cores may be copper coated so that the glass insulator when plastic will wet the surfaces of the core and plug and form a gas-tight seal. When employing ordinary lead glass as the insulating material the core may consist of a nickel-iron alloy having a somewhat lower coefficient of expansion than lead glass and provided with a copper coating. Other copper coated metals may, of course, be similarly used if desired in order to make the seal gas-tight. Theassembled cores, insulators and plug are heated to a temperature at which the glass is plastic but not fluid and the seal'is then swaged to reduce the diameter of the shell and insulators, thus providingx a firm adherence of the insulators with t e cores and plug 10. Seal 4 is then inserted into the container 1 and fused. to the end thereof in any suitable manner. The seal fits snugly within container l and the outwardly extending flange 11 permits the application of a high temperature at the outer edge of the discharge device without causing injury to the insulating material of the seal.

According to the present invention, I have found that the probability of cracks in a seal of the above type may be greatly diminished and the voltage insulation raised to any degree desired by forming the seal of alternate layers or shells of thin glass and very thin metal. Referring to Fig. 3, I have indicated at 12, 13 and 14 a plurality of spaced, successively enclosing lead glass cylinders having substantially the same coeflicient of expansion as copper. A plurality of nested copper cylinders 15 and 16, approximately 5 mils in thickness, separate the glass cylinders from one another. A conductive core 17, similar to cores 6 and 7, is threaded through the inner glass cylinder 12 and may provide the anode element 3 of the rectifier. The alternate layers of insulating material and copper are placed in a copper coated ferrous metal cylinder or shell 18 having an outwardly. extending flange 19 similar to that indicated at 11 on the seal 4. The shell 18 is approximately one eighth of an inch thick and provides a ood mechanical support for the glass cylin ers, while the cylinders 15 and 16 are thin enough to permit plastic deformation thereof when the Ill The assembled shell 18 and the concentric layers of glass and metal are heated to a temperature of about 800 C. or until the glass is plastic but not fluid, after which the seal is swaged, thereby reducing the diameter of shell 18 and the glass insulators, and forming a gas-tight seal between the metal parts of the seal and the glass insulators. The seal 5 may then be fused to container 1 at the end thereof in any suitable manner.

The glass cylinders 12, 13 and 14 should have a thickness less than one tenth of their length. I have found that glass having a thickness of approximately and a length of approximately 1" gives very satisfactory results. Obviously, the type of seal shown in Fig. 3 could be employed at both ends of the container 1 if desired. Furthermore, while I have illustrated a seal formed by a swaging operation, it is obvious that the seal may be produced in various other ways. For example, I have found that good seals may be formed by forcing glass under pressure between concentric metal surfaces. Seals made by the latter method are likely to be more uniform than those made by swaging and can very readily be built up to any desired size.

lVhat I claim as new and desire to secure by Letters Patent of the United States 1s:-

1. A gas-tight seal for electrical devices comprising a plurality of cylindrical layers of glass and a plurality of cylindrical layers of metal, the glass layers being spaced from one another by the metal layers, each layer of glass making a gas-tight joint with the adjoining metal surface.

2. A gas-tight seal for electrical devices aeeesrss comprisin a central core of conductive material, a lurality of cylindrical layers of glass an a plurality of cylindrical layers of metal surrounding said core, the glass layers being spaced from one another by the metal layers, each layer of glass making a gas-tight joint with the adjoining metal surace.

3. A gas-tight seal for electrical devices comprising an outer cylindrical shell of metal, a core of conductive material spaced from the shell, and a series of alternate successivelv enclosing shells of vitreous material an metal between said outer shell and core.

4. A gas-tight seal for electrical devices comprising a plurality of spaced concentric metal cylinders, a core of conductive material spaced from the inner cylinder and a mass of vitreous material lilling the space between the concentric cylinders and the space between the conductor and inner cylin- 5. A gas-tight seal for electrical devices comprising a series of alternate layers of metal and glass, the metal being thin enough to permit plastic deformation when the glass layers expand.

(S. A gas-tight seal for electrical devices comprising an outer cylindrical shell of metal, a core of conductive material spaced from the shell, and a series of alternate successively enclosing shells of vitreous material and metal filhng the space between said outer shell and core.

In witness whereof, I have hereunto set my hand this 21st day of August, 1926.

ALBERT W. HULL. 

